This invention relates to a top chord member used in the construction of the sidewalls of a gondola or hopper type railway car. It relates particularly to an aluminum top chord member especially suitable for railway cars constructed substantially of aluminum sheet and plate. It also relates to an aluminum top chord member especially adapted for use in railway cars which are unloaded in a rotary car inversion unloading device or in a vibrating shakeout machine both of which facilitate the unloading of bulk material from the car.
Open top gondola or hopper type railway cars are generally comprised of a metal floor, sidewalls and end walls. While such cars have most frequently been made of steel, many cars are being made substantially of aluminum sheet and plate to reduce the overall weight of the car and thereby increase its carrying capacity. The sidewalls of the gondola and hopper cars are stiffened and reinforced by a plurality of spaced, parallel, vertical side posts. A longitudinal top chord member extends along the tops of each sidewall and the side posts to further strengthen the sidewalls of the car.
Open top gondola railway cars that are used to carry bulk materials, such as coal, are frequently unloaded in a rotary car dumper which is a device that clamps onto the top chords of the sidewalls of the car and rotates the entire car and its contents to an inverted position to quickly unload the contents. Another unloading device, often used for hopper cars, is a car shaker that also clamps onto the top chords of the sidewalls of the car and imparts vibrating or shaking forces to the car to dislodge its contents and facilitate its unloading. Both of these car unloading devices impart concentrated and unusual localized forces to the top chord members of the car.
In the past, railway car designers have recognized the need for special top chord members to accept these unloading operations.
U.S. Pat. Nos. 2,748,723, and 4,561,361 disclose hot rolled steel bulb sections which are especially designed to accommodate rotary car dumpers or car shaker devices. While these rolled bulb sections have proven satisfactory for cars and top chord members made of steel, they have lacked sufficient strength and integrity when used for aluminum cars and top chord members. U.S. Pat. No. 4,840,127 is an example of a top chord member designed especially for use in aluminum gondola or hopper cars in which the top chord member is a rectangular, tubular extrusion having a thickened stem portion to better resist bending moments where the top chord is fastened to the sheets and posts that make up the sidewall of the car. Such a top chord, while more suitable for aluminum cars than the rolled bulb angle, lacks sufficient strength and integrity for extended use in the rotary or shaker type car unloading devices.